However, 30-year-old Joshua Hupperterz did not plead guilty to the murder charge against him.
Hupperterz is accused of killing 22-year-old Jenna Burleigh in the summer of 2017.
His guilty pleas on Tuesday were for abuse of a corpse and tampering with evidence.
Assistant District Attorney Jason Grenell said in his opening statements Tuesday that evidence will show Hupperterz beat and strangled Burleigh after she objected to a sex act, the Associated Press reports.
Hupperterz still contends his roommate, who has not been charged or implicated by police, killed Burleigh.
Investigators say Hupperterz killed Burleigh in his Philadelphia apartment early Aug. 31, 2017, then moved her body to his mother's suburban home in a plastic storage container.
In court, prosecutors said Burleigh tried to defend herself by grabbing a knife, which Hupperterz then allegedly stabbed her with before strangling her.
Joshua Hupperterz pleaded guilty to abuse of corpse and tampering with evidence and pleaded not guilty to murder and possession of instrument of crime in Jenna Burleigh case.— Katherine Scott (@KScott6abc) January 8, 2019
Investigators say he later moved Burleigh's body to his grandmother's home in the Poconos, where the body was discovered.
Hupperterz faces a mandatory sentence of life in prison with no parole if convicted of first-degree or second-degree murder.
The Associated Press contributed to this report
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